1. Technical Field of the Invention
The present invention relates to multiple access communications and, in particular, to the transmission of code division multiple access modulated signals over bundled copper wire pairs in a public switched telephone network.
2. Description of Related Art
During the initial introduction of telecommunications exchanges, all telecommunications subscribers were connected with their servicing telecommunications exchange via a copper wire pair, also referred to herein simply as xe2x80x98pairxe2x80x99, which formed an individual physical path to the servicing telecommunications exchange. For each physical path, a trench had to be dug in which to lay the copper wire pair. However, due to the rapid increases in the numbers of telecommunications subscribers, the number of physical paths required quickly became numerous and unmanageable.
The foregoing problem was alleviated by bundling individual copper wire pairs into a single physical path to the servicing telecommunications exchange. Individual copper wire pairs would lead from a termination point at the subscriber""s premises to a nearby aggregation point. At the aggregation point, many copper wire pairs serving nearby subscribers are bundled together and laid in a single physical path. Additionally, several bundles may intersect at another aggregation point and be further bundled together and laid in a single physical path to a serving telecommunications exchange.
Degradation in the quality and clarity of the transmitted signal to the subscriber can occur due to either variable and changing transmission qualities of the copper wire pair or cross-talk. Cross-talk occurs when a signal transmitted on one copper wire pair creates an electromagnetic field which induces a current in a different copper wire pair which interferes with the signal transmitted on the different copper wire pair. Cross-talk is effected by three factorsxe2x80x94distance between the copper wire pairs, insulation of the copper wire pairs, and the power of the transmitted signal. Bundling the copper wire pairs inherently increases the likelihood of cross-talk. Although copper wires are well insulated, cross-talk still occurs when the transmission power of a signal is high. Accordingly, the transmission power must be limited to prevent cross-talk. Limiting the transmission power, however, reduces the bit transmission rate of a digital signal.
Additionally, degradation in the transmission quality can occur as a result of changes or deterioration in the transmission properties of the copper wire pair. The problem due to failure of the copper wire pair are usually solved by switching the affected subscriber to an unused copper wire pair or, where no unused copper wire pair exists, laying a new copper wire pair. Identifying, swapping, and laying copper wire pairs is an expensive operation.
Furthermore, traditional transmissions over individual pairs are capacity inefficient in the sense that when the subscriber unit is idle, the pair is likewise idle and, in such a state, represents an untapped bandwidth potential between the idle subscriber and the central office. In other words, the local loop between a subscriber and a central office has conventionally been implemented as a dedicated circuit. When the user is not making communications over the respective copper wire pair, that pair is idle and the pair capacity is simply wasted. A multilink transmission engaging all available pairs in a multiplexing scheme could utilize the intrinsic capacity of each pair thus providing greater bandwidth to the active subscribers at a given moment by exploiting the transmission capacity of the otherwise idle pairs.
Accordingly, it is a first object of the present invention to maintain an acceptable level of transmission quality while minimizing the need to identify, swap and lay new copper wire pairs due to failure or degradation of individual copper wire pairs.
It is another object of the present invention to more efficiently exploit the intrinsic capacity of existing wire pairs in a pubic switched telephone network.
It is yet another object of the present invention to employ bundled copper wire pairs as a multilink transmission medium in a public switched telephone network.
It is still another object of the present invention to provide code division multiple access modulation over bundled copper wire pairs in a public switched telephone network.
It is still another object of the present invention to provide greater bandwidth to individual subscribers of a public switched telephone network for digital communications without increasing the number of copper wire pairs employed for such communications.
It is still another object of the present invention to allow failure of an individual or plurality of copper wire pairs in a bundled set of copper wire pairs without interruption or failure of services to any individual subscribers.
These and other objects are addressed by the merits of the present invention as described in the forthcoming detailed description and accompanying figures contained hereinbelow.
The present invention is directed to a system and method for transmitting a signal from a telephone terminal to a central office. The telephone terminal and central office are connected to aggregation points. The aggregation points include wire hoppers which receive the signals from the telephone terminal and the central office, spread the signals over a plurality of communication channels and transmit the signals over a common multilink transmission medium. When the signals are received at the central office, they are, accordingly, reassembled.